• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.43-47
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• 2001

A numerical parametric study is conducted to simulate shock-induced combustion with a variation in freestream conditions. The analysis is limited to inviscid flow and includes chmical nonequilibrium. A steady combustion front is established if the freestream Mach number is above the Chapman-Jouguet speed of the mixture. On the other, an unsteady reaction fi:ont is established if the freestream Mach number is below or at the Chapman-Jouguet speed of the mixture. The three cases have been simulated for Machs 4.18, 5.11, and 6.46 with a projectile diameter of 15 mm. Machs 4.18 and 5.11 shows an unsteady reaction front, whereas Mach 6.46 represents a steady reaction front. Thus Chapman-Jouguet speed is one of deciding factor for the instabilities to trigger. The instabilities of the chemical front with a variation of projectiles diameters will be investigated.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1527-1533
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• 2011

The reaction of gas-phase atomic hydrogen with oxygen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. We have calculated the probability of the OH formation and energy deposit of the reaction exothermicity in the newly formed OH in the gas-surface reaction H(g) + O(ad)/Si${\rightarrow}$ OH(g) + Si. All reactive events occur in a single impact collision on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability is dependent upon the gas temperature and shows the maximum near 1000 K, but it is essentially independent of the surface temperature. The reaction probability is also independent upon the initial excitation of the O-Si vibration. The reaction energy available for the product state is carried away by the desorbing OH in its translational and vibrational motions. When the initial excitation of the O-Si vibration increases, translational and vibrational energies of OH rise accordingly, while the energy shared by rotational motion varies only slightly. Flow of energy between the reaction zone and the solid has been incorporated in trajectory calculations, but the amount of energy propagated into the solid is only a few percent of the available energy released in the OH formation.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.3
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• pp.10-17
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• 2017

The analytical modeling has been established on the self-propagation of intermetallic reaction in the spanwise direction of highly reactive boron and titanium nanoscale multilayers. Assuming that the reaction obeys Arrhenius kinetics, two-dimensional computations are carried out for heat and atomic species diffusion with exothermic reaction model in order to simulate the self-propagation of intermetallic reaction. The effects of bimetallic layer thickness and thickness ratio on the reaction propagation speed are tested and discussed in addition to the assessment of pre-mixing zone effects.

• Korean Journal of Veterinary Research
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• v.29 no.2
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• pp.11-18
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• 1989

This study was undertaken to obtain basic data of the sternal development in Korean native cattle from the earliest sternal formation to the ossification using histological and histochemical methods. Thrity three sterna were collected from a series of embryos and fetuses ranging from 11 to 225mm (estimated age 37~120days) in crown rump length. The bilateral sternal bars were observed in the 2nd group(CRL 21~3mm) of Korean cattle embryos. Those bars initiated to be fused in the 3rd group (CRL 31~4mm) and completed in the 7th group(CRL 71~80mm). The ossification centers were detected in the 8th group(CRL 81~90mm) also bilateral ossification centers were found in the same group. The typical epiphyseal plates, endochondral bone and calcium deposit were found in the 9th group(CRL 91~100mm). Osteocytes, osteoblasts, osteoclasts and myeloid cells appeared in ossification centers in the 10th group(more than CRL 101mm). The alcianophility responded markedly in the 9th group that was decreased and showed slightly positive reaction in territorial matrix of the 10th group. Marked positive reaction to PAS was observed in bony trabeculae in the 10th group. The positive reaction to calcium deposit by trichrome stain was observed initially in the hypertrophied zone of epiphyseal plate in the 9th group and was conspicuous in the calcified zone of epiphyseal plate in the 10th group. The 1st positive reaction to the von Kossa stain was observed in the 9th group.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.950-958
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• 2002

The combustion characteristics of a low NOx burner using reburning technology have been experimentally studied. The return burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NOx is mainly produced in a primary combustion zone and a certain portion of NOx can be converted to nitrogen in the rebury zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/reburn fuel ratio, the primary/secondary air ratio, and the injection location of rebury fuel and secondary air. When the amount of return fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NOx formation of stoichiometric condition at a primary combustion zone is nearly independent of the rebury conditions (locations, fuel/air ratios) while the NOx emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NOx emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.31-43
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• 2008

Oxy-fuel flame has a significantly different structure from that of air-fuel flame because of its high temperature. This study is aimed to find out the difference of the oxy-fuel flame structure in order to understand reaction mechanism closely, which is crucial to design real-scale oxy-fuel combustion system. By examining pictures of counterflow flame and LIF images, we found that oxy-fuel flame had two-zone structure: fuel decomposition region and distributed CO oxidation region. In the oxy-fuel flame, OH radical was distributed intensely through the whole flame due to its higher flame temperature than crossover temperature. For showing those features of the oxy-fuel flame, 1 MW scale IFRF oxy-natural gas burner was simulated by conditional moment closure(CMC) model. Calculation results were compared with experimental data, and showed agreements in trend. In the simulated distributions of fuel decomposition/CO oxidation rates, CO oxidation region was also separated from fuel decomposition zone considerably, which showed the two-zone structure in the oxy-fuel flame.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1269-1279
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• 1995

An experimental study is carried out on turbulent diffusion flames stabilized by a circular cylinder in a divergent duct flow. A commercial grade gaseous propane is injected from two slits on the rod as fuel. Flame stability limits, as well as size and temperrature of recirculation zone, are measured by direct and schlieren photographs to clarify the characteristics and structure of diffusion flames and to assess the effect of various divergent angle of duct. The results of the present study are as follows. Temperature in the recirculation zone decreases with increasing divergent angle. The blow-off velocity in parallel duct is higher than that in divergent duct. Critical blow-off velocity is expected to be about 8-12 degree through blow-off velocity pattern. Regardless of divergent angles, the length of recirculation zone is nearly constant, and this length becomes longer with rod diameter. Pressure gradient has an effect on the eddy structure in shear layer behind the rod. With the increase of divergent angle, large scale eddies by dissipated energy in shear layer are split into small scale eddies, and the flame becomes a typical distributedreacting flame.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.4
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• pp.34-41
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• 1995

The structure of premixed tubulent flames in a constant-volume vessel was investigated using a schlieren method and microprobe method. The schlieren method was used to observe the flame structure qualitatively. The microprobe method, which detects a flamelet by detecting its flame potential signal, was used to investigate the deeper flame structure behind the flame front. The flame potential signal having one to six peaks was obtained in the case of turbulent flames, each of them being regarede as a flamelet existing in the flame zone. Based on this consideration, the flame propagation speed, the thickness of the flame zone, the number of flamelets and the separation distance between adjacent flamelets in the flame zone were measured. Moreover, the thickness of flamelet which could not be attempted in the conventional electrostatic probe method was also investigated. The experimental results of this work suggest the existence of "reactant islands" in the reaction zone, and show that the averaged number of flamelets increases with an increase in the turbulence intensity and/or a decrease in the Damkohler number. The mean thickness of flamelet in the case of turbulent flames was found to be about two times compared to laminar values.ar values.

• Korean Journal of Veterinary Research
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• v.33 no.2
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• pp.189-198
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• 1993

The present study was undertaken to provide basic data on endochondral ossification for the axis in developing Miniature Schnauzers. This study was determined to the morphological features and development of growth plast in the axis of this experimental animals by histological and histochemical methods. The axis from 2 healthy Miniature Schnauzers(postnatal 6hr, 5week) was used. The obtained results were as follows : 1. In 5-week-old Miniature Schnauzer, the axis consisted of 4 separate ossification centers : centrum l, intercentrum 2, centrum 2 and epiphysis. Intercentrum 2 was intercalated between centrum 1 cranially, centrum 2 caudally. 2. The space of centrum 1 was more broader than the other ossification centers. 3. The zone of reserved chondrocytes was more extensive than the zone of proliferative chondrocytes, trabeculation was weakly observed, however, the proximal epiphyseal plate of axis was actively trabeculation observed in the zone of calcified chondrocytes. 4. Eighteen columns of chondrocytes were observed in the centrum 1 and five to seven columns of chondrocytes were observed in the centrum 2 of Miniature Schnauzer(postnatal 5 week) 5. A positive reaction to alcianophility was observed in all the territorial matrix at the zone of hypertrophic chondrocytes in this experimental animals.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.2
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• pp.1-1
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• 1992

YIG(Yttrium Iron Garnet) single crystals were grown by FZ(Floating Zone) method. Since YIG melts incongruently, TSFZ(Traveling Solvent Floating Zone) method which was modified FZ was applied to grow YIG single crystals. The optimum growth condition were growth rate Imm/hr, counter-rotation 30rpm and oxidized atmosphere was necessary to sintering and growth process. The quality of grown crystals depended on the degree of sintering. The voids were generated by the reaction of Fe ions with oxygen and the density of voids was increased with the growth rate increased. When the growth rate was more than 1.5mm/hr, the cellular growth occured and the density of dislocation was increased at the periphery of crystals. Also, secondary phases of orthoferrite(YFe$O_3$)compost ion were observed in the grown crystal.